PEOFESSOE OWEN ON THE SPECIES OP PHASCOLOIHTS. 357 



The. lower incisors of Phascolomys latifrons are more distinct in size and shape from 

 those of Fhascolomys platyrhinus than are the upper ones. The vertical diameter of 

 the transverse section (PI. LVII. fig. 5) is the longest, not the transverse diameter 

 (ib. fig. 4). The outer surface (fig. 5, a), vertical, and slightly channelled, is divided 

 by a well-marked angle from the lower surface (J), which is slightly and transversely 

 convex. The enamel covering the lower surface bends over the angle dividing it from 

 the outer surface and there stops (at a). In Fhascolomys ])latyrMnus (ib. fig. 4) the 

 lower enamelled surface (ib. V) bends up upon the outer [a) to near the upper surface, 

 terminating there at an angle or ridge. A narrow longitudinal groove representing 

 the wider outer channel in the hairy-nosed Wombat, divides the enamelled outer angle 

 from the flat upper surface. The transverse section of the incisor may be called trian- 

 gular in both species ; but the base is internal and the apex external in Fhascolomys 

 platyrhinus, while the base is inferior and the apex superior in JPhascolomys latifrons. 

 The lower incisors are likewise smaller relatively to the jaw and to the molar teeth 

 in the hairy-nosed than in the bare-nosed Wombat ; and this character is more strongly 

 marked in the large extinct Wombats indicated in my second Memoir on the osteology 

 of the Marsupialia'. 



The first lower molar, on the other hand, is as large in Phascolomys latifrons (PI. LVII. 

 fig. 7, d 3) as in Phascolomys platyrhinus (ib. fig. 6, d 3) ; it is consequently larger in pro- 

 portion to the size of the species, and in proportion to the other molar teeth ; it has also a 

 different form. In Phascolomys platyrhinus the transverse section and working surface 

 of d 3, (fig. 6) is usually a full ellipse, with the long axis nearly parallel with that of the 

 jaw. In Phascolomys latifrons the section is subquadrate (fig. 7). The anterior surface 

 {e) usually shows a feeble longitudinal groove ; the outer surface is rather narrower 

 than the other three. The enamel covering it extends a short way upon the front 

 surface, and then, after an interruption, is resumed upon the antero-intemal angle: 

 the outer enamel extends uninterruptedly over two thirds of the hinder surface. The 

 other bUobed or biprismatic molars show little more than the difference of size, the 

 four {d 4, m i, 2, 3, fig. 3) equalling in longitudinal extent three and a half of those in 

 Phascolomys platyrhinus (fig. 1). In all the species the enamel is wanting on the inner 

 side of the tooth, which is nearly on a level with the inner wall of the alveolus ; the 

 outer wall is lower and exposes more of the tooth ; the curves of the positions of the 

 prismatic surfaces are reversed in the upper and lower molars. 



Mr. Waterhouse, in his instructive paper on the Dentition of the Flying Opossums', 

 pointed out two subgenera as having four true molar teeth on each side of both jaws, and 

 a third subgenus as having three true molars on each side of both jaws ; but the obser- 

 vations on marsupial modifications of dentition were not carried further in that paper. 



In January 1839 I communicated my paper on the classification of the Marsupialia", 



' Trans. Zool. Soc. vol. iii. (1845), p. 306. ' Proc. Zool. Soc. 1838, p. 149. 



2 Trans. Zool. Soc. vol. ii. p. 315. 



